For a mechanical seal, which is an example of a sliding component, to maintain sealing property for a long period of time, it must satisfy the mutually exclusive conditions of “seal” and “lubricate.” Particularly in recent years, the demand for lower friction is increasing further in the area of environmental protection, etc., as a means to prevent the sealed fluid from leaking while reducing mechanical loss at the same time. One way to reduce friction is to generate dynamic pressure between the sealing faces by means of rotation to create the so-called fluid lubrication state where the surfaces slide against each other with a liquid film in between. In this case, however, positive pressure generates between the sealing faces and the fluid flows out of the sealing faces from the part subject to the positive pressure. This is the so-called lateral leak that occurs with bearings and corresponds to how seals leak.
In the case of liquid seal, where the viscosity of the liquid is greater than that of gas, the dynamic pressure effect is achieved between the two surfaces due to their minute undulations and surface irregularities that are present even when both are planes. Accordingly, liquid seal structures are often designed to give priority to sealing performance. On the other hand, however, several mechanisms have been contrived to demonstrate the pumping effect of pulling back the leaked liquid to the high-pressure side in order to seal and lubricate at the same time. For example, Patent Document 1 discloses an invention which is a rotating ring having several spiral grooves on its shaft seal area in the circumferential direction so as to move the fluid toward the high-pressure chamber.
Also among other inventions relating to a sliding component, one invention is known where a suction means is formed on the sealed-fluid side of the sealing face in order to introduce the sealed fluid to the sealing face, and the sealed fluid thus introduced is stored in two dimples formed on the outer periphery side and inner periphery side of the sealing face in the radial direction and separated by a dam, while being pumped into the dimple on the inner periphery side in the radial direction, so as to prevent leakage of the sealed fluid from the seal area positioned on the inner periphery side of the two dimples in the radial direction (refer to Patent Document 2).
However, the invention described in Patent Document 1 above are subject to a pressure difference between the inner periphery and outer periphery of the seal or other sealing face, thus requiring a pumping action to counter the pressure and are potentially unable to push back the fluid depending on the level of this pressure. This creates the problem of inevitable increase of fluid leakage rate when the pressure difference is large, although leakage can be prevented when the pressure difference is small. Also, according to the invention described in Patent Document 2, excessive pumping effect of the dimple on the sealed-fluid side increases the leakage rate, while excessive pumping effect of the dimple on the atmosphere side makes the sealed fluid disappear from the seal area, thereby causing these dimples formed on the seal area to directly contact the sealing face on the mating side to increase the torque. Prior Art 2 presents a problem in that, although the pumping effects of the respective dimples must be balanced in order to prevent the leakage rate from increasing and also prevent the torque from increasing, doing so is quite difficult in reality.